Cellular dichotomy between anchorage‐independent growth responses to bFGF and TPA reflects molecular switch in commitment to carcinogenesis

Abstract

We have investigated gene expression patterns underlying reversible and irreversible anchorage-independent growth (AIG) phenotypes to identify more sensitive markers of cell transformation for studies directed at interrogating carcinogenesis responses. In JB6 mouse epidermal cells, basic fibroblast growth factor (bFGF) induces an unusually efficient and reversible AIG response, relative to 12-O-tetradecanoyl phorbol-13-acetate (TPA)-induced AIG which is irreversible. The reversible and irreversible AIG phenotypes are characterized by largely nonoverlapping global gene expression profiles. However, a subset of differentially expressed genes were identified as common to reversible and irreversible AIG phenotypes, including genes regulated in a reciprocal fashion. Hepatic leukemia factor (HLF) and D-site albumin promoter-binding protein (DBP) were increased in both bFGF and TPA soft agar colonies and selected for functional validation. Ectopic expression of human HLF and DBP in JB6 cells resulted in a marked increase in TPA- and bFGF-regulated AIG responses. HLF and DBP expression were increased in soft agar colonies arising from JB6 cells exposed to gamma radiation and in a human basal cell carcinoma tumor tissue, relative to paired nontumor tissue. Subsequent biological network analysis suggests that many of the differentially expressed genes that are common to bFGF- and TPA-dependent AIG are regulated by c-Myc, SP-1, and HNF-4 transcription factors. Collectively, we have identified a potential molecular switch that mediates the transition from reversible to irreversible AIG.

Inhibition of ERK oscillations by ionizing radiation and reactive oxygen species

“…ERK oscillations might correlate with the regulation of an unidentified tumor suppressor activity. In support of this statement, bFGF regulates ERK oscillations and a reversible anchorage‐independent growth (AIG) response in JB6 mouse epidermal cells [1, 32]. How bFGF prevents acquisition of the malignant phenotype remains unknown, however, independent investigators have demonstrated that bFGF does not function as a tumor promoter alone or in combination with TPA in mouse skin [33, 34].…”

Genetic Analysis Identifies the Role of HLF in Renal Cell Carcinoma

“…However, HLF can also transactivate c-JUN to promote tumor initiating cell-like properties of hepatoma cells by reactivating SRY-box transcription factor 2 and POU class 5 homeobox 1 (33). Ectopic HLF expression was shown to increase anchorage-independent growth and inhibit cell death in JB6 mouse epidermal cells (34). These observations raise the possibility that HLF may have different roles during tumorigenesis in a tissue-and context-specific manner.…”

ERK Oscillation-Dependent Gene Expression Patterns and Deregulation by Stress Response

“…14 We have defined gene expression patterns that are unique to bFGF in JB6 cells and not associated with the fully transformed JB6 phenotype (RT101 cells). 14 We have analyzed this data set and identified tumor suppressors unique to bFGF-dependent ERK oscillations (lysyl oxidase, 35 ≈7-fold ↑; aspartoacylase 2, 36 ≈9-fold ↑; insulin-like growth factor binding protein 5, 37 ≈9-fold ↑; and scavenger receptor class A, member 5, 38 ≈7-fold ↑). In human keratinocytes (Figure 2B), ERK oscillations were uniquely associated with increased tumor suppressor mRNA expression, including PDCD6, 39 CD44, 40 WNT7A, 41 HOPX, 42 WNT5A, 43 and others.…”

“…13 The mechanisms by which ERK oscillations are deregulated in vitro remain unclear; however, these observations suggest that the oscillating phenotype is under-represented in cell culture models used for toxicological investigations. ERK oscillations regulate a tumor suppressor activity that is conserved in vitro / in vivo , 14 suggesting that oscillatory behavior can significantly impact biological outcomes. Therefore, it is prudent to consider this regulatory feature in toxicological investigations, and there is a need to bridge the molecular dynamics observed in vitro with complex biology in tissues to improve the interpretation of experimental models used for hazard assessment and risk prediction.…”